1. Field of the Invention
The invention relates to a process for obtaining a hard coated article having anti-fouling properties, especially an optical article such as an ophthalmic lens, comprising a substrate coated with a hard coating providing good abrasion resistance and hardness and good adhesion to the anti-fouling coating and the article such obtained.
2. Description of Related Art
It is a common practice in the art to coat at least one main surface of a lens substrate, such as an ophthalmic lens, with several coatings for imparting to the lens substrate additional or improved optical or mechanical properties. These coatings are designated in general as functional coatings.
Thus, it is usual practice to coat at least one main surface of a lens substrate, typically made of an organic glass material, with successively, starting from the surface of the lens substrate, an abrasion- and/or scratch-resistant coating (hard coat), an anti-reflection coating and an anti-fouling top coat that will prevent the adhesion of stains or will render easier the removal of stains.
However, it has been difficult up to now to provide an article having a hard coat and an anti-fouling coating deposited directly thereon because it is particularly difficult to obtain a good adhesion between the hard coat and the anti-fouling coating.
JP 2000-308846 describes a method intending to solve the problem of forming an anti-fouling layer on a base material, such as an optical part, which has excellent anti-fouling properties, scratch-resistance and solvent resistance.
According to this method, before forming said anti-fouling layer, at least one surface of the base material which is to be treated is pre-treated and the anti-fouling layer is formed on this pre-treated surface.
The pre-treatment involves the following methods: high frequency discharge plasma method, electron beam method, ion beam method, vapor deposition method, sputtering method, alkali treatment method, acid treatment method, corona treatment method or atmospheric pressure glow discharge method.
Practically, the pre-treatment is made on an inorganic layer of an anti-reflection coating.
Document US 2005112365 (TDK Corporation) addresses specifically the problem of adhesion between an anti-fouling top coat and a hard coating and discloses a substrate having:                a hard coating composition comprising a silicon compound or a hydrolyzate thereof;        a layer of an anti-staining and/or lubricating functional material that comprises a silicon compound deposited thereon and adhering to the hard coat.        
The substrate can be an optical lens and the silicon compounds of the hard coat are organic alkoxy silanes.
The hard coating composition may comprise organic compounds that polymerize and cure upon irradiation with active energy rays.
As examples of such organic compounds, the above referred TDK Patent Application cites monomers and oligomers of organic compounds that undergo cationic polymerization such as epoxy compounds and organic compounds comprising one or more unsaturated double bond used in a ratio of 10 to 2000 parts by weight per 100 parts by weight of silicon compound in the hard coating composition.
According to the process described in US Patent Application 2005112365, the hard coating composition is half cured, i.e. is partially cured. Then the anti-fouling coating composition is deposited and the obtained stack is further cured by heating to get a final product.
In practice, in the examples of the above referred TDK Patent Application, the hard coating is not half-cured but simply dried so as to remove the solvent.
A disadvantage of this technique is that the properties of the top coat may be decreased.
Accordingly, there is still a need of providing a process for improving the adhesion of an anti-fouling top coat to a hard, abrasion-resistant coating.